Oral glucose tolerance test within the scope of prenatal care: Evaluation 2010–2012

Introduction

A pregnancy-associated, impaired glucose tolerance leads to increased morbidity in the child and the mother. A link between elevated glucose levels during pregnancy and complications affecting the infant has been sufficiently described in the literature [1–9].

In January 2010, Austria included the oral glucose tolerance test in the prevention program for pregnant women in weeks 24–28 of gestation. The care of pregnant women and the implementation of examinations during pregnancy are mainly handled by resident gynecologists.

The cut-off values of the 75 g/2 h oral glucose tolerance test (OGTT) were based on the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study and set by a commission of experts (OGTT; international consensus criteria). The metabolic situation should be assessed at the very beginning of pregnancy, if one or several risk factors, as well as clinical symptoms indicate the presence of diabetes [10]. If gestational diabetes is diagnosed during pregnancy, an oral glucose tolerance test (2 h/75 g; measurement of fasting and 2 h plasma glucose levels) should be carried out again 6–12 weeks after delivery. OGTT should be repeated every 2 years (WHOcriteria), if the results do not confirm the risk of diabetes. If the test yields pathological results, preventive and/or therapeutic measures will be initiated.

Materials and methods

Over a period of 3 years (January 2010–December 2012), gynecologists referred 3963 pregnant women to our residental laboratory. The province of Salzburg recorded 15,227 births from the beginning of January 2010 to the end of December 2012. The percentage of all pregnant women who came to our laboratory for a 2 h/75 g OGTT was 26%. OGTTs administered before the 24^th and after the 28^th week of pregnancy (i.e., outside the screening period, e.g., suspected GDM or GDM in early pregnancy) were not included.

Thirty-one tests had to be discontinued prematurely, and were therefore not included in the statistics either: three patients had fasting glucose levels of ≥7 mmol/L, which gave rise to the suspicion of preexisting diabetes mellitus. Twenty-eight pregnant women ended the test prematurely due to nausea or vomiting. After birth, tests were conducted on 335 GDM patients for the purpose of reclassifying the glucose metabolism (HbA_1c, FPG, OGTT) and were done until the end of March 2013.

Implementation of 2 h/75 g-OGTT: After fasting for at least 8 h, the pregnant women were subjected to a standardized glucose tolerance test at our laboratory in the morning. Fasting venous plasma was collected, pre-tested by means of POCT, and if the blood glucose levels were <7 mmol/L, 75 mg glucose was administered. The liquid was sipped in a maximum of 5 min. Additional blood samples were drawn after 1 and 2 h. During this time, the pregnant patient waited in a quiet, seated position. The venous blood was obtained using the Vacuette^® blood collection system (Greiner Bio-One, Kremsmünster, Austria). The tubes contain sodium fluoride as a glycolysis inhibitor and K₃ EDTA as an anticoagulant. The sample thus collected was tested immediately. After a 15-min centrifugation at 2500×g, the supernatant plasma was obtained, and the glucose was measured using a Cobas^® Modular Analyzer (Roche Diagnostics, Basel, Switzerland). A quality-assured in-vitro test was used. The analysis was done according to the hexokinase method. The cut-off value was: fasting, ≥5.1 mmol/L; after 1 h, ≥10 mmol/L; after 2 h, ≥8.5 mmol/L. Gestational diabetes occurs when at least one of the three limits was reached or exceeded.

Results

Between January 2010 and December 2012, 3963 pregnant women were examined. Elevated glucose levels were detected in 335 individuals (8.5%) (Table 1). In 201 women (5.1%), pathological glucose fasting levels were revealed regardless whether glucose levels after 1 h or 2 h were elevated. In 134 patients (3.4%) elevated glucose levels were only detected by determination of the glucose values after 1 h and/or 2 h (Table 2). A reclassification of the glucose metabolism after birth by means of OGTT, as proposed by the WHO, was observed in 4.2% (14 of 335 women) of the GDM patients. In 13.1% (44 of 335) of these women, at least one fasting glucose and/or HbA_1c measurement was taken.

Discussion

Treatment of gestational diabetes leads to a significant reduction of metabolic related diseases in the child [11, 12]. Therefore, an effective, cost-efficient and suitable screening method for pregnant women is needed. The present method facilitates the early diagnosis of gestational diabetes, but is only partly cost-efficient and patient-friendly. Our data show that an FPG analysis captures 60% of pregnant diabetic women, while 40% of the patients went undetected without oral glucose tolerance testing. Promising, multi-level models of GMD diagnostics have already been developed on the basis of fasting glucose measurements in order to lower the number of OGTTs (e.g., FPG measurement and risk stratification using OGTT only when necessary [13]). In this regard, further scientific research is still needed to find a sensible, low-impact alternative for pregnant women.

The number of OGTTs performed at our laboratory 6–12 weeks after birth following GDM (WHO criteria) is strikingly small. It is clear that effective GDM screening in conjunction with consistent care of patients constitutes a good basis for the reduction of complications and costs.

Conflict of interest statement

Authors’ conflict of interest disclosure: The authors stated that there are no conflicts of interest regarding the publication of this article.

Research funding: None declared.

Employment or leadership: None declared.

Honorarium: None declared.